Procedure for shelling of crustaceous shellfish, especially shrimps, and apparatus for performance of the procedure

ABSTRACT

An apparatus for shelling shellfish such as shrimps consists of a dosing chamber (3) and a heat treatment chamber (5) separated by a slide valve (11) and sealed by cylindrical membrane valves (7, 9). From a funnel (31) the shellfish fall down into the dosing chamber (3) whose valve (7) is closed. The slide valve (11) is opened and a portion of animals fall down into the heat treatment chamber (5), whose bottom is closed by another membrane valve (9). The slide valve (11) is closed and steam at high pressure and temperature is induced into the heat treatment chamber (5). The pressure is removed from the membrane valve (9) after which the standing overpressure in the chamber (5) blows the shellfish out of the discharge opening (19) towards a rebound plate (35). Hereby the meat and shells of the shellfish are separated.

The invention concerns a method for shelling crustaceous shellfish,especially shrimps and prawns, where the shrimps after having beenboiled and cooled, are being heated and then exposed to a pressurereduction and are transported to strike against a surface of solidmaterial so that the shells cf the shellfish are separated from themeat, and an apparatus intended for performing the method, where theapparatus comprises one pressure-tight sealable chamber provided with atleast one valve, said chamber having an opening near the bottom fordischarge of crustaceous shellfish and where in the connection with theapparatus there is furnished at least one in proportion to the directionof movement of the shellfish tilted rebound plate for separation of theshellfish's meat and shells.

Such a method and such an apparatus are known from DK patent applicationNo. 2149/87 where the shellfish in a process plant after boiling andcooling, during which the shellfish absorb a large amount of water, aretransported through a heating tun and after which they fall down intofunnels, whose outlets lead to a vacuum chamber. Between the outlets andthe chamber there are membrane valves which are opened and closed in alaid down stroke so that the shellfish in small amounts at a time falldown into the vacuum chamber. The liquid, or the meat juice, in theheated shellfish is brought to the boiling point by the vacuum treatmentso that the shells are loosened from the meat and when the shellfishinside the chamber hit the rebound plates or similar, the shells areknocked off the meat of the shellfish. Then the meat and the shells falldown into a transport liquid which is sucked out through the bottom ofthe chamber. In a later process the shells are separated from the meatin a wind separation unit.

However, because of the vacuum treatment in connection with the liquidtransport from the chamber, the meat looses part of the meat juice,which reduces the meat's quality of taste.

The purpose of this invention is to provide a procedure for shellingshellfish, such as shrimps, during which juice and taste from the meatis lost in a much lesser degree without the process thereby being slowerand thus more expensive to utilize.

According to the invention, this is obtained by a procedure of the sortas stated in the introduction, a procedure which is distinctive becauseof the fact that the shellfish in portions in a pressure-tight chamberat the same time are being heated and exposed to an increase of pressureby the chamber having induced one or more warm and pressurized gasesand/or wet steam, upon which the pressure reduction and the movementtowards the surface of solid material is provoked by opening a valve inthe chamber opposite the surface.

By using the procedure according to the invention, excess pressure isbeing used causing the gases in the chamber to penetrate the surface ofthe shellfish at the same time as juice and absorbed liquid from theboiling is being heated right under the shell. During the followingequalizing of the pressure, the liquid and the juice boil coincidingwith the shellfish being flung against a surface of a rebound plate,which stands in the path of the shellfish's movement out of the chamber.By using the method according to the invention, meat and shells mayhereby be lead away without using a transport liquid.

It is preferred to perform the procedure as stated in claim 2, where thetemperature of the steam and/or the gases is between 110° and 150° C.,and where the volume of their absolute pressure ranges from 1.5 to 5bar, equivalent to an overpressure of 0.5 to 4 bar. The stay in thepressure-tight chamber can hereby be reduced to less than 10 seconds.

In a preferred embodiment of the invention, the procedure is performedas mentioned in claim 3, where, in the pressure-tight chamber withinmax. 0.1 second by the use of dry saturated steam, a static overpressureis built up to a volume between 2.1 and 3.1 bar. Hereby an exceptionalefficient shelling of the shellfish is obtained.

The invention also concerns an apparatus intended for performing themethod, where the apparatus comprises one pressure-tight sealablechamber provided with at least one valve, said chamber having an openingnear the bottom for discharge of crustaceous shellfish and where in theconnection with the apparatus there is furnished at least one inproportion to the direction of movement of the shellfish mounted tiltedrebound plate for separation of the shellfish's meat and shells.

The apparatus in accordance with the invention makes a specialpreheating tun as used by the known technique unnecessary, and isfurthermore considerably simpler in the same functions than those of theknown apparatus, as you do not have to lead transport liquid through thechamber. Removal of shell parts and meat can take place on conveyorbelts.

In order to achieve a higher process speed than that of the knowntechnique, you can build the apparatus as mentioned in claim 5, where adosing chamber is fitted under the membrane valve, the chamber having avolume equal to the amount of shellfish to be treated at the same time,and being placed above the pressure-tight sealable chamber and separablefrom the pressure-tight sealable chamber with a slide valve, thedischarge opening being provided with a membrane valve and placed in thebottom cf the chamber.

When fitted with an automatic control, the apparatus can in accordancewith this embodiment shell shrimps and similar shellfish at aconsiderable speed, as the shellfish by conveyor belt are led to thefunnel on the top of the apparatus. Here they fall down into the dosingchamber whose membrane valve is open. At the same time the slide valveis closed and the dosing chamber is filled with shellfish. The membranevalve is closed so that no more shellfish can fall down at the sametime, while the membrane construction does not damage the shellfishwhich are in the valve and the slide valve is opened. Then the shellfishcan fall down into the pressure-tight chamber, the slide valve isclosed, steam/gases at a suitable temperature and pressure are inducedand after a suitable period of time, the lower membrane valve is openedby removing the pressure behind the membrane. The shellfish are thusshot out of the pressure chamber at high speed because of the excessivepressure in the chamber, by means of which the shells are pushed off themeat.

An embodiment of the invention is further described below with referenceto the drawing where

FIG. 1 shows a schematic drawing of a sectional elevation through anapparatus according to the invention,

FIG. 2 shows five different working steps for the apparatus when usingthe method according to the invention.

The apparatus according to the invention may in a preferred embodimentconsist of blocks with square cross sections stacked on top of eachother and through which coaxial holes are drilled for formation of adosing chamber 3, a heating chamber 5, a dosing valve 7 and a dischargevalve 9. Between dosing chamber 3 and a heating chamber 5, a slidingvalve 11 is provided depending on a pneumatic cylinder 13 can shut offthe heating chamber 5 from the dosing chamber 3. Seals 15 are fitted sothat a relative overpressure from the heating chamber 5 will press thevalve 11 against the seals 15.

The dosing and discharge membrane valves 7 and 9 consist of cylindricpieces of material with elastic properties (elastomer material), asshown in FIG. 1 in their inactive position, and which can be brought toshut off the inlet and outlet openings 17 and 19 respectively by the useof compressed air conducted through the connecting branches 21 and 23.

Steam in an overheated or wet condition can be conducted to the heatingchamber 5 through a connecting branch 25 from which the steam isconducted through a ring-shaped distribution chamber 27 to openings 29in the chamber 5.

A receiving funnel 31 may lead boiled and cooled shellfish from aconveyor belt 33 to the apparatus. A rebound plate 35 is situatedoutside the discharge opening 19, and a conveyor belt 37 can removeprocessed shellfish and shell parts for further treatment. The reboundplate 35 can be made from a smooth stainless steel plate which is fittedto the apparatus. Other types of surfaces are acceptable within theframes of the invention, e.g. rough, chequered or other types ofstructuralized surfaces, and the material may have elastic properties orbe synthetic.

When using the method according to the invention, the apparatus works asshown in FIG. 2, where the designations (a) to (e) indicate differentstages of the shelling process.

In condition (a) the dosing chamber is filled with shellfish, the slidevalve 11 and the dosing valve 7 are closed. Any shellfish stuck betweenthe membranes in the valve 7 are not damaged in this condition becauseof the membrane construction where the closing mechanism is provided bythe pneumatic pressure behind the membranes.

In condition (b) the valve is open and the shellfish have fallen downinto the heating chamber 5, the bottom of which is closed by thedischarge valve 9. In condition (c), the valve 11 is closed again anddry saturated steam is induced at a pressure between 2.2 and 3.0 baroverpressure for a period between five and seven seconds. The openings29 and the ducts from there to the ring-shaped chamber 27 and to theconnecting branch 25 are dimensioned so that the pressure in the chamber5 is built up very quickly, i.e: during a time period of magnitude about0.01 second. During the heating, which continues in condition (d), thedosing valve 7 is opened and a new portion of shellfish may fall fromthe funnel 31 down into the chamber 3. Hereafter, in condition (e), thepressure is removed from the discharge valve 9, upon which the standingpressure in the chamber 5 will blow the contents of the chamber outtowards the plate 35. After this, both valves 7 and 9 are closed and theprocess may continue as (a).

The apparatus itself may be designed in several ways. Several apparatuscan advantageously be placed together, e.g. in a circle where thedischarge openings face a circular conic rebound plate. The membranevalves do not, as described here, have to be cylindrical, as themembrane might bear against a wall in each valve opening which e.g.might be semicircular with a straight side instead of being cylindrical.

Within the frames of the invention, the procedure might be performedusing other apparatus than that of this description. The heating chambercould be left with one valve opening, acting as both inlet and dischargeopening and the apparatus could be turned or shifted with its openingfacing alternately a receiving funnel or filling branch and a rebounditem. Alternatively, the apparatus itself could wholly or partly befixed and the receiving funnel and the rebound means could be moved inproportion to the opening.

We claim:
 1. A method for shelling crustaceous shellfish, comprising thesteps of(a) boiling and cooling the shellfish, (b) introducing theshellfish into a pressure-tight chamber (5) and heating the shellfish inthe pressure-tight chamber while exposing the shellfish when within saidchamber to an increase of pressure, (c) opening a valve (9) to saidchamber, to cause a pressure reduction in said chamber, and (d) causingthe shellfish to exit said chamber after opening of said valve andstrike against a surface (35) of solid material so that the shells ofthe shellfish are separated from the meat.
 2. A method according toclaim 1 in which method step (b) includes heating and increasingpressure with at least one warm and pressurized gas.
 3. A methodaccording to claim 2 in which heating is to a temperature of between110° and 150° Celsius, and increasing pressure is from between 1.5 and 5bar absolute pressure.
 4. A method according to claim 4 in which methodstep (b) includes heating and increasing pressure with wet steam.
 5. Amethod according to claim 4 in which heating is to a temperature ofbetween 110° and 150° Celsius, and increasing pressure is from between1.5 and 5 bar absolute pressure.
 6. A method according to claim 5 inwhich step (b) includes creating within said chamber within a maximum of0.1 second a static overpressure of from between 2.1 and 3.1 bar. 7.Apparatus intended for shelling crustaceous shellfish, comprising apressure-tight sealable chamber (5) provided with at least one valve,said chamber (5) having an opening (19) near the bottom for discharge ofcrustaceous shellfish and including at least one tilted rebound plate(35) oriented at an angle relative to the direction of movement ofshellfish in said apparatus for separation of the shellfish's meat andshells, in which the chamber (5) includes means for inducing gasesand/or wet steam with pressure and temperature higher than those of thesurrounding atmosphere and the discharge opening (19) includes anothervalve (9) to release the discharge opening (19) momentarily, saidopening (19) facing the rebound plate (35).
 8. Apparatus according toclaim 7 further including a funnel (31) located to direct the shellfishto a membrane valve (7) in the top side of the apparatus, and having adosing chamber (3) fitted under the membrane valve (7), the dosingchamber (3) having a volume equal to the amount of shellfish to betreated at the one time and being located above the pressure-tightsealable chamber (5) and separable from the pressure-tight sealablechamber (5) by a slide valve (11).